Cuttlefish In Love

Maritime mating tricks.

For all the men out there who think they planned something clever for Valentine's Day, consider the ingenuity of the male Australian cuttlefish. With males outnumbering females by up to 10-1 on their spawning grounds, they're forced to go the extra mile. While the large males can simply guard a female and fight off small males, little guys have come up with their own little trick: They disguise themselves as females.

"Why would he want to turn into a female?" asks Marine Biological Laboratory scientist Roger Hanlon. "The reason is that the big males would like to have additional mates."

Hanlon has spent five spawning seasons with the Australian cuttlefish, and he says small males sometimes use the same camouflage trick that allows them to escape predators—changing their shape and color—to mimic a female and swim right past a large male.

"And as soon as he gets under the big male and he's next to the female, it's like, 'Okay! Let's try a mating,'" he says. "And this is the incredible thing is that the female mates with those mimics at a higher percentage than she does with other males."

Considering that females reject 70 percent of all mating attempts, this is no small feat. Hanlon says "sexual mimicry" like this is common in other animals, but since he and his team took DNA samples from the fish and their progeny, his report in the journal Nature provided the first genetic evidence of sexual mimicry successfully resulting in offspring.

As for why it works, he can only guess.

"Maybe there's an advantage to that female to get some of his genes. Maybe he's a pretty clever guy," he guesses. "There's something attractive, clever, some sign of fitness, of that male doing something clever, that may be an indirect sign of good genes in that animal. And so she will take the gamble, if you will, of mating with him and taking his DNA in the hope that he's a good match for her."

But before you consider this another notch on the belt for brains over brawn, keep in mind that any trick can backfire. Hanlon says the visual deception by the male "mimics" is so convincing that the large males will sometimes try to mate them.